System of compressing a log stream using a scratch pad of logically deleted entries

ABSTRACT

Managing a log stream of a computer system. An entry of a log stream, desired to be removed from the log stream, but not eligible for removal, is logically deleted. Logical deletion keeps the entry on the log stream and indicates that the entry can be removed from the log stream when it is eligible. When the entry is eligible, it is removed. If a desired entry remains at the tail of the log stream for a given period of time, thus not allowing the removal of one or more undesired entries, the desired entry is rewritten to the head of the log stream and deleted from the tail. Thereafter, other logically deleted entries eligible for deletion are removed from the log stream.

TECHNICAL FIELD

This invention relates, in general, to the management of a log streamand, in particular, to the deleting of unnecessary entries from the logstream and to the compressing of the log stream.

CROSS REFERENCE TO RELATED APPLICATIONS

This application contains subject matter which is related to the subjectmatter of the following application, which is assigned to the sameassignee as this application and filed on the same day as thisapplication. The below listed application is hereby incorporated hereinby reference in its entirety:

"Tail Compression Of A Log Stream Using A Scratch Pad Of LogicallyDeleted Entries," by Clark et al., Ser. No. 08/827,560, (Docket No.PO9-96-094).

BACKGROUND ART

In various computer systems, historical log data is maintained (forexample, in log files) for use in system recovery, problem determinationand/or system maintenance. Typically, these log files have a limitedamount of capacity to retain the historical data. After the capacity ismet, at least some of the data records are moved from the log files toexternal storage devices, such as direct access storage devices (DASD),thereby providing additional space in the log file for more data.

At some point, data within the log file and/or on the external storagedevices are no longer needed. For example, there is no need to keep thedata once it passes its retention requirements. The saving of data pastits usefulness adversely affects system performance in a number of ways.For example, when unnecessary data is retained and the log file needs tobe browsed to recover logged data during recovery of a failure, thebrowser may have to deal with potentially large amounts of unnecessarydata, thereby slowing down the recovery process. Additionally, when thesaving of unwanted data records requires the use of external storagedevices, which typically provide slower access to the data, the readingof the data takes longer, thus, affecting system performance.

Therefore, it is beneficial to delete any unnecessary data from the logfiles. However, generally, there are a number of restrictions placed onwhat data can be deleted. In one example, data may only be deleted fromthe tail of the log file. Thus, if the data record at the tail is stillnecessary, then no data can be deleted from the log file. This forcesthe saving of many unnecessary or unwanted data records.

The above problem is exacerbated when a log file is shared by multiplesystems and the data record at the tail is owned by a system that hasfailed. In that case, the data record may not be deleted for a very longtime, if at all, causing the saving of an increasing number of unwanteddata records.

Thus, a need exists for a technique that allows the removal ofunnecessary data records from a log file, even when the data record atthe tail is still wanted. A further need exists for a technique thatallows the removal of data records by the non-owner of the data records.A yet further need exists for a log management capability that cancompress a log file in an efficient manner.

SUMMARY OF THE INVENTION

The shortcomings of the prior art are overcome and additional advantagesare provided through the provision of a system of managing a log stream.The system includes, for example, means for identifying an entry of thelog stream that is not eligible for removal from the log stream; and aprocessor adapted to logically delete the entry from the log stream. Thelogical deletion keeps the entry on the log stream and indicates thatthe entry can be removed from the log stream when it is eligible to beremoved.

In one example, the system includes a scratch pad adapted to indicatethe logical deletion of the entry. The scratch pad is separate from thelog stream.

In a further example, the processor is also adapted to remove the entryfrom the log stream when the entry is eligible for removal. In oneembodiment, the processor includes a resource manager not owning theentry, and the resource manager is adapted to initiate the removal ofthe entry from the log stream.

In another aspect of the present invention, a system of managing a logstream is provided, which includes means for logically deleting oneentry from the log stream when the entry is ineligible for removal fromthe log stream; means for removing another entry from the log stream, inwhich the removing causes the one entry to be eligible for removal; andmeans for removing the one entry from the log stream, subsequent toremoval of the another entry.

In yet a further aspect of the present invention, a system of managing alog stream is provided which includes a resource manager adapted toinitiate a rewrite of a first entry from one location of the log streamto another location of the log stream, when the first entry is to atleast temporarily remain on the log stream. The resource manager isfurther adapted to initiate deletion of the first entry from the onelocation.

The log management capability of the present invention advantageouslyprovides for the logical deletion of unnecessary log entries on a logstream, such that the logically deleted entries can subsequently beremoved from the log stream by any resource manager connected to the logstream. The technique of the present invention allows the removal ofunnecessary data records from the log stream, even when the entry at thetail is still wanted. The invention advantageously provides for therewriting of the entry at the tail to another location within the logstream, so that unnecessary entries can be deleted. Additionally, thelog management capability of the present invention enables the efficientcompression of the log stream, in which additional log streams are notnecessary.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other objects, features, andadvantages of the invention will be apparent from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 depicts one example of a computer system incorporating and usingthe log stream management capability of the present invention;

FIG. 2 depicts one example of a log stream of the computer system ofFIG. 1, in accordance with the principles of the present invention;

FIG. 3a depicts one example of a logical deletion vector of the computersystem of FIG. 1, in accordance with the principles of the presentinvention;

FIG. 3b depicts one embodiment of a resource management vector of thecomputer system of FIG. 1, in accordance with the principles of thepresent invention;

FIG. 4 depicts an embodiment of the logic used to logically delete anentry from the log stream of FIG. 2, in accordance with the principlesof the present invention;

FIGS. 5a-5b depict an updated logical deletion vector and an updatedresource management vector, respectively, in accordance with theprinciples of the present invention;

FIG. 6 depicts one embodiment of the logic used to compress the logstream of FIG. 2, in accordance with the principles of the presentinvention; and

FIG. 7 depicts one example of a log stream in which an entry at the tailof the log stream has been moved forward of the tail, in accordance withthe principles of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

In accordance with the principles of the present invention, a log streammanagement capability is provided in which tail compression is performedon a log stream of a computer system without requiring the creation ofother log streams. A scratch pad is maintained within the computersystem to identify logically deleted, but not yet physically deletedentries, and this scratch pad is used during the tail compression, asdescribed herein.

One example of a computer system incorporating and using the log streammanagement capability of the present invention is depicted in FIG. 1 anddescribed in detail herein. In one example, computer system 100 is basedon the Enterprise Systems Architecture (ESA)/390 offered byInternational Business Machines Corporation, and includes one or moreprocessors 102 coupled to a coupling facility 104. Each processor 102includes an operating system 106 and one or more resource managers 108,each of which is described below.

In one embodiment, operating system 106 is, for instance, the MultipleVirtual Storage (MVS) operating system offered by International BusinessMachines Corporation (or the OS/390 operating system offered byInternational Business Machines Corporation), and includes a systemlogger component 110. In particular, in one example, the system loggerruns in its own address space started by the operating system. Thesystem logger is used for the log stream management capability of thepresent invention, as described below, and one embodiment of a systemlogger is described in MVS Programming Assembler Services Reference, IBMPublication No. GC28-1910-01 (September 1996); and MVS ProgrammingAssembler Services Guide, IBM Publication No. GC28-1762-01 (September1996), each of which is hereby incorporated herein by reference in itsentirety.

Each of resource managers 108 owns and controls a set of resourceswithin the computer system. For example, a resource manager can be adatabase management facility, such as IMS or DB2, or a communicationsfacility such as Advanced Programming To Programming Communications(APPC), all of which are offered by International Business MachinesCorporation.

As mentioned above, each processor is coupled to coupling facility 104.Coupling facility 104 is a shareable facility that contains storageaccessible by the processors and performs operations requested by theresource managers and/or programs running within the processors. In oneembodiment, coupling facility 104 is a structured-external storageprocessor (SES). Examples of a coupling facility are described in detailin U.S. Pat. No. 5,317,739, entitled "Method and Apparatus for CouplingData Processing Systems," by Elko et al., issued May 31, 1994, and inU.S. patent application Ser. No. 08/632,683 entitled, "Method And SystemFor Log Management In A Coupled Data Processing System," by Geiner etal., filed on Apr. 15, 1996, both assigned to International BusinessMachines Corporation, and each of which is hereby incorporated herein byreference in its entirety.

In accordance with the principles of the present invention, couplingfacility 104 includes a log stream 112. (Coupling facility 104 mayinclude a plurality of log streams, and one or more of those log streamscan be managed, in accordance with the principles of the presentinvention.) In one example, log stream 112 is accessible by each of theprocessors and capable of containing one or more entries for each of theprocessors. In one embodiment, at least a portion of log stream 112 canbe stored in one or more storage devices (e.g., direct access storagedevices (DASD)), when, for example, sufficient space for the log streamno longer exists within the coupling facility.

One example of a log stream and various services corresponding to thelog stream are described in detail in U.S. patent application Ser. No.08/632,683 entitled, "Method And System For Log Management In A CoupledData Processing System," by Geiner et al., filed on Apr. 15, 1996, whichis hereby incorporated herein by reference in its entirety.

One example of the components of log stream 112, used for the presentinvention, are described in detail with reference to FIG. 2. In oneembodiment, log stream 112 includes a number of log blocks or logentries 200, each having a respective block identifier 202. Each blockidentifier corresponds to, for instance, a relative offset into the logstream. Data and other various information may also be included in thelog stream, but need not be discussed for the present invention.

In addition to the above, FIG. 2 depicts for each log entry anidentifier 204 of the resource manager owning that log entry. Forexample, in the log stream of FIG. 2, the identifier "RM2" identifiesthat Resource Manager 2 owns the log entry corresponding to blockidentifier "005." Furthermore, "XX" indications are included for variouslog blocks, which indicate that those entries are logically deleted, asdescribed more fully below. The identifiers 204 and the XX markings donot appear in the log stream, but are shown in FIG. 2 for illustrativepurposes, only.

One end of log stream 112 is referred to herein as the tail or rear ofthe log stream. In one embodiment, the rear of the log stream typicallyincludes the oldest entry of the log stream (i.e., the entry with theoldest block id). The other end of the log stream is referred to hereinas the head, which is forward from the tail or rear. (In anotherembodiment, it may be the head instead of the tail, which typicallyholds the oldest entry. The present invention equally applies to such alog stream.)

The log stream described above is only one example. In anotherembodiment, the log stream can include log data for just a singlesystem. Additionally, the log stream need not be included in a couplingfacility. It can be, for instance, located in main storage, a cache,auxiliary storage, external storage devices, or any combination thereof.

A computer system can have various log streams, including multisystem orsingle log streams, or a combination of both, and one or more of thoselog streams can be managed in accordance with the principles of thepresent invention. The log stream of a system can be stored in onemedium or a combination of various media, including but not limited to,a coupling facility, main storage, a cache, auxiliary storage, orexternal storage devices.

Referring back to FIG. 1, in one example, according to the presentinvention, coupling facility 104 further includes a scratch pad 114 thatis used by the log management capability of the present invention, asdescribed herein. In one example, the scratch pad is created by thefirst system logger that attempts to read the scratch pad. In oneembodiment, scratch pad 114 includes two vectors: a logical deletionvector 300 (FIG. 3a), and a resource management vector 302 (FIG. 3b),each of which is described in detail herein.

In one embodiment, logical deletion vector 300 includes a number ofentries 302 that have been logically deleted from log stream 112, butnot yet physically deleted (removed), as described in detail below. Eachentry 302 includes, for instance, a block id 304, which corresponds toblock id 202 of the log entry to be deleted, and a next LDE index 306,which is an index to the next logically deleted entry for that resourcemanager, if there is one. For example, entry 3 of vector 300 (FIG. 3a)indicates that block identifier "005" has been logically deleted. Entry3 of vector 300 further indicates that the next logically deleted entryfor the resource manager owning block id 005 is at entry 4 of vector300. Entry 4 corresponds to block id 009. This corresponds to FIG. 2, inwhich block id 005, marked as XX, is owned by RM2 and the next block idowned by RM2, marked with XX, is block id 009.

As mentioned above, in one embodiment, scratch pad 114 further includesresource management vector 302, one example of which is depicted in FIG.3b. Resource management vector 302 includes one or more entries 308, andeach entry includes, for example, an identifier 309 and an LDE index310. Identifier 309 identifies the name of the resource manager owningthe log block corresponding to the block id of vector 300 specified byindex 310. For example, entry 3 of vector 302 indicates that ResourceManager 3 owns the block id represented in entry 5 of vector 300 (i.e.,block id 004).

In accordance with the principles of the present invention, resourcemanager vector 302 includes only one entry for each resource managerhaving logically deleted entries on the log stream. In particular, itincludes the most rearward logically deleted entry for the resourcemanager. In order to find the chain of logically deleted entries for aparticular resource manager, logical deletion vector is used.

In accordance with the principles of the present invention, scratch pad114 is used in the logical deletion of entries from log stream 112. Inone embodiment, entries are logically deleted from the log stream whenthey are no longer needed but cannot be physically deleted or removedfrom the log stream for one reason or another. For example, if an entryis not at the tail (rear) of the log stream (e.g., block id 002 of FIG.2), then it cannot be physically deleted, even if it is no longerneeded. Additionally, as another example, if the entry to be deleted isthe only entry on the log stream, then it also cannot be physicallydeleted. Thus, it would be logically deleted, in accordance with thepresent invention.

One embodiment of the logic used to logically delete an entry from logstream 112 is depicted in FIG. 4 and described in detail herein.Referring to FIG. 4, initially, an inquiry is made as to whether the logblock to be deleted (i.e., either physically or logically) from the logstream is at the rear (tail) of the log stream, INQUIRY 400. Inparticular, one of the resource managers determines that it no longerneeds one or more blocks on the log stream. Thus, the resource managerchecks to see if the oldest block it no longer needs is the block at thetail of the log stream. In one example, this check is made by requestingfrom the system logger the id of the block at the tail.

If the log entry is not at the tail, then the entry cannot be physicallydeleted (i.e., removed), so it is logically deleted by the resourcemanager writing information corresponding to the log entry to scratchpad 114. In particular, the block id of the block to be logicallydeleted is stored in vector 300 and its corresponding resource manager,if this is the first logically deleted block for that resource manager,is stored in vector 302. If there is another entry in vector 300 for thesame resource manager, then an indication of such will be made in thecolumn labelled "NEXT LDE ENTRY." Thereafter, logical deletion of theblock is complete, STEP 404.

If, on the other hand, the log block to be deleted, INQUIRY 400, is theblock at the tail of the log stream, then a further determination ismade as to whether it is the only log block on the log stream, INQUIRY406. If it is, then it cannot be physically deleted, so it is logicallydeleted, as described above, STEP 402.

However, when the log block to be deleted is the log block at the rearof the log stream and it is not the only log block on the log stream,the log block is physically deleted, STEP 408. In one example, physicaldeletion is carried out by system logger 110, which is informed of theblock to be deleted by the resource manager wanting to delete the block.One example of physical deletion of a log block is described in detailin MVS Programming Assembler Services Reference GC28-1910-01; and MVSProgramming Assembler Services Guide GC28-1762-02, each of which ishereby incorporated herein by reference in its entirety. Thereafter,deletion of the log block is complete, STEP 404.

In one aspect of the present invention, the resource manager instructingthe physical deletion of the rearmost log entry, can further have one ormore additional logically deleted entries, as identified by the scratchpad, physically deleted by the system logger. In particular, when theowning resource manager deletes its log entry, it determines byexamination of logical deletion vector 300 that one or more otherentries have been logically deleted, and thus, can be physicallydeleted. In one embodiment, these entries are organizationallycontiguous blocks in the log stream to the most rearward entry. As oneexample, if block id 001 is deleted from log stream 112 of FIG. 2, thenblock ids 002-005 can also be deleted, even though those blocks may beowned by a different resource manager. In one embodiment, all of theseblocks can be deleted only if there still remains one log block on thelog stream, which is true in this one particular example. Once theseblocks are deleted, block id 006 becomes the new rear of the log stream.

In another aspect of the present invention, whenever any of resourcemanagers 108 initiates physical deletion and/or logically deletes logentries 200, the particular resource manager updates logical deletionvector 300 and/or resource management vector 302, to accurately reflectthe deletion by that particular resource manager. This updatingpreferably occurs after physical deletion of the rearmost log entry, aswell as after any continuation of the physical deletion with respect tologically deleted entries 302, as discussed above. Examples of vectors300 and 302 after they are updated to reflect the deletion of block ids001-005 are depicted in FIGS. 5a, 5b, respectively.

In accordance with the principles of the present invention, if theresource manager owning the entry at the tail of the log stream needs toretain that entry for a long period of time, it is possible that one orboth of the logically deleted entry vector and the resource managervector will fill up. To prevent this situation, a threshold point isestablished. The threshold value is, for example, 50% of the capacity ofthe logically deleted entry vector. In one embodiment, the thresholdvalue or limit is stored within the coupling facility and thus,accessible by each of the resource managers coupled to the couplingfacility. (In another embodiment, copies of the threshold value can bestored within each processor, instead of or in addition to the couplingfacility. In yet another embodiment multiple threshold values can bestored within the coupling facility and/or within the processors andused, as described herein.) The threshold value is used in determiningwhen the log stream is to be compressed, as described in detail withreference to FIG. 6.

One example of the logic used in compression of the log stream isdepicted in FIG. 6 and described in detail herein. Initially, adetermination is made as to whether the capacity of the scratch pad hasreached a preselected relationship with respect to the threshold value,INQUIRY 600. This preselected relationship can include, for example, adetermination that the logical deletion vector has reached or exceededits preselected threshold value of, for example, fifty percent. If thescratch pad has not reached its preselected limit, then processing flowsback to INQUIRY 600 to repeat the determination at preselected timeintervals.

In particular, in one example, a compression timer established by eachresource manager, when the resource manager connects to the log stream,pops every 5 seconds, as one example, thereby informing the resourcemanager to check whether the entry at the tail is owned by that resourcemanager. If it is, then that resource manager checks the logicaldeletion vector against the threshold. When the owning resource managerdetects that the threshold has been reached, it performs the compressiondescribed below.

When the limit has been reached, a further determination is made as towhether the log block at the rear or tail of the log stream represents alogically deleted block, INQUIRY 602. This determination is made by theowning resource manager, which, in one example, checks to see whetherthe log block at the rear of the log stream is included in logicallydeleted entry vector 300.

When the log block at the rear has not been logically deleted, the logblock at the rear is written forward of the rear, STEP 604. In oneembodiment, the resource manager initiates the rewriting of the logentry to the head of the log stream (i.e., the least rearward positionin the log stream), gives the rewritten log entry a new block id, andinitiates the deleting of the original entry off of the tail. (In oneexample, the system logger does the physical writing and deleting fromthe log stream under instruction of the resource manager.) When an entryis given a new block id, it is considered herein as a new entry, eventhough the data located in the entry may be older than the data of otherentries.

As one example, since block id 001 of FIG. 2 has not been logicallydeleted, it is moved to the head, as shown in FIG. 7. Thereafter,processing continues at INQUIRY 600, "IS SCRATCH PAD AT THRESHOLD?"

However, when the rear block is a logically deleted block (such as blockid 002 of FIG. 7 after, for instance, block id 001 has been moved to thehead), then that block is physically deleted, as described above, STEP606. Subsequently, the log block is removed from scratch pad 114, asdescribed above, STEP 608.

In one embodiment of the present invention, physical deletion of theother logically deleted entries at the rear (e.g., block ids 003-005)continues until there are no further logically deleted entries at therear, and as long as one entry remains in the log stream. However, inanother embodiment, the physical deletion occurs only until the logicaldeletion vector falls below its prespecified limit.

In a further aspect of the present invention, if the resource managerowning the entry at the tail loses its connection to the log stream dueto, for instance, system failure or resource manager failure, one of theother resource managers connected to the log stream will detect thissituation by determining that the entry at the tail is still the sameafter two consecutive compression cycles (using, e.g., a counter). Thus,the resource manager detecting this situation will have the blockrewritten to the head of the log stream, as described above, afterobtaining global serialization of the computer system (e.g.,SCOPE(SYSTEMS)ENQ). This take over mechanism allows performance of thetail compression using just one multisystem log stream.

Described above in detail is a log management facility that enables tailcompression to be performed on a multisystem log stream by any of theresource managers connected to the log stream. The tail compression doesnot require the creation or maintenance of another log stream, nor anincrease in the size of the log stream. Instead, it uses a scratch padto keep track of logically deleted entries, some of which may bephysically deleted during the compression. Additionally, the presentinvention permits tail compression for entries owned by failed resourcemanagers.

The computer system described above is only one example. The presentinvention can be used and/or incorporated within other systems orenvironments without departing from the spirit of the present invention.For example, different architectures and/or operating systems can beused without departing from the spirit of the present invention. As afurther example, each processor can include one or more operatingsystems. As another example, one or more central processing complexes iscoupled to the coupling facility, and each central processing complexincludes one or more central processing units, which executes anoperating system. Further, in another embodiment, the computer systemcan include multiple coupling facilities and/or multiple scratch pads.Additionally, the present invention is applicable to computer systemswith only one processor and with systems that do not include a couplingfacility. In yet a further embodiment, the system logger can be aseparate component from the operating system. Again, the computer systemdescribed herein is only one example.

As described above, a log stream includes one or more datum (e.g., logdata). Thus, other entities that include one or more datum are includedwithin the definition of a log stream. These entities include, but arenot limited to, log files and log data sets.

The present invention can be included in an article of manufacture(e.g., one or more computer program products) having, for instance,computer useable media. The media has embodied therein, for instance,computer readable program code means for providing and facilitating thecapabilities of the present invention. The article of manufacture can beincluded as a part of a computer system or sold separately.

The flow diagrams depicted herein are just exemplary. There may be manyvariations to these diagrams or the steps (or operations) describedtherein without departing from the spirit of the invention. Forinstance, the steps may be performed in a differing order, or steps maybe added, deleted or modified. All of these variations are considered apart of the claimed invention.

Although preferred embodiments have been depicted and described indetail herein, it will be apparent to those skilled in the relevant artthat various modifications, additions, substitutions and the like can bemade without departing from the spirit of the invention and these aretherefore considered to be within the scope of the invention as definedin the following claims.

What is claimed is:
 1. A system of managing a log streamcomprising:means for identifying an entry of said log stream that is noteligible for physical removal from said log stream, wherein said meansfor identifying comprises means for determining whether said entry isineligible for physical removal, said means for determiningcomprising:means for determining whether said entry is located at oneend of said log stream; and means for determining, when said entry is atsaid one end, whether said entry is an only entry of said log stream,wherein said entry is not eligible for physical removal when it is notat said one end or when it is said only entry; anda processor adapted tologically delete said entry from said log stream, said logical deletionkeeping said entry on said log stream and indicating that said entry canbe physically removed from said log stream when it is eligible to bephysically removed.
 2. The system of claim 1, further comprising ascratch pad adapted to indicate said logical deletion of said entry,said scratch pad being separate from said log stream.
 3. The system ofclaim 2, wherein said scratch pad comprises:a logical deletion vectorcomprising an identifier of said entry; and a resource manager vectorcomprising an identification of a resource manager owning said entry. 4.The system of claim 1, wherein said one end is a tail of said logstream.
 5. A system of managing a log stream comprising:means forlogically deleting one entry from said log stream when said entry isineligible for physical removal from said log stream, said logicaldeleting comprising keeping said entry on said log stream and indicatingthat said entry can be physically removed from said log stream when itis eligible for physical removal; means for removing another entry fromsaid log stream, said removing causing said one entry to be eligible forphysical removal; and means for physically removing said one entry fromsaid log stream, subsequent to removal of said another entry, whereinsaid means for physically removing said one entry comprises a resourcemanager, not owning said one entry, initiating said physical removal. 6.The system of claim 1, wherein said processor is further adapted tophysically remove said entry from said log stream when said entry iseligible for physical removal.
 7. The system of claim 6, wherein saidprocessor comprises a resource manager not owning said entry, saidresource manager being adapted to initiate said Physical removal of saidentry from said log stream.
 8. The system of claim 6, wherein saidprocessor is further adapted to physically remove from said log streamone or more additional entries previously logically deleted from saidlog stream, when said one or more additional entries is eligible forphysical removal.
 9. The system of claim 6, further comprising one ormore resource managers adapted to initiate physical removal from saidlog stream of one or more additional entries previously logicallydeleted from said log stream, when said one or more additional entriesis eligible for physical removal.
 10. The system of claim 9, wherein atleast one resource manager does not own at least one of the entries itis initiating the physical removal thereof.
 11. The system of claim 6,further comprising a scratch pad of logically deleted entries, saidscratch pad updated to remove any indication within said scratch pad ofsaid entry, after said physical removal.
 12. The system of claim 1,further comprising a resource manager adapted to initiate physicalremoval of said entry from said log stream when said entry is eligiblefor physical removal.
 13. The system of claim 1, wherein said one end isa tail of said log stream.
 14. A system of managing a log streamcomprising:means for logically deleting one entry from said log streamwhen said entry is ineligible for physical removal from said log stream,said logical deleting comprising keeping said entry on said log streamand indicating that said entry can be physically removed from said logstream when it is eligible for physical removal; means for removinganother entry from said log stream, said removing causing said one entryto be eligible for physical removal; and means for physically removingsaid one entry from said log stream, subsequent to removal of saidanother entry.
 15. The system of claim 14, further comprising means forphysically removing any other previously logically deleted entries fromsaid log stream that are eligible for physical removal.
 16. The systemof claim 15, wherein said means for physically removing of any otherpreviously logically deleted entries comprises a resource managerinitiating physical removal of at least one entry of said previouslylogically deleted entries, said resource manager not owning said atleast one entry.